November 23, 2010: The AAVSO requests ground-based observations of the Trapezium region of the Orion Nebula (M42), along with surrounding regions in Orion, in conjunction with upcoming observations with the MOST Satellite. All AAVSO observers are encouraged to participate in this project, and we are requesting observations for a number of different targets from both instrumental and visual observers.

This observing program headed by Dr. Matthew Templeton is exploring low-amplitude variability in bright stars of the Trapezium using the Canadian satellite MOST (Microvariability and Oscillations of Stars)[1]. This is an exploratory proposal to search for low-amplitude variability in these young stars due to any number of potential causes: pulsations, magnetic activity and rotation, or accretion processes are all possible. MOST will be capable of measuring the light curves of many stars in the Trapezium with precision better than 1 mmag. The observations will be conducted at some point during the December 2010 - January 2011
time-frame, and will span approximately one month. We are requesting observations before, during, and after the observing window, and several of the targets are worthwhile long-term monitoring objects as well. Observers from multiple longitudes are especially encouraged. Since this is an equatorial source, both northern and southern hemisphere observers are encouraged to participate.

Intensive time series are not required for any of these projects, but good precision photometry should be the primary goal. Observers are also strongly encouraged to transform their observations to a standard system if it is at all possible for them to do so. For more information on obtaining your transformation coefficients, see Gordon Sarty's guide to transformations available via the AAVSO website along with the CCD observing manual:

We also encourage observers to be consistent in using the same apertures when performing aperture photometry of their sources. Visual observers should make sure to be oriented at the eyepiece the same way for all observations of a star. The detection of low-amplitude variations will depend upon removing any and all sources of systematic variation.

Finally, please *do not* use the old Harvard Designations for any of these objects; identify them with GCVS name *only*.

Ground-based observations are requested for the following:

1) High-precision, photometric observations of the bright eclipsing binary star BM Ori (V ~ 8.0; RA: 05 35 16.15 , Dec: -05 23 06.5). We request filtered observations of this star to better understand the nature of the eclipsing object. Two to three cycles of BVRI measurements per night are encouraged, in order to provide good coverage of the 6.5-day variation. Given the brightness of the object we strongly encourage high-S/N observations, but please be careful not to saturate.

2) Time-series observations of fainter sources in the field. There are a number of fainter sources in and around the Trapezium region, many of which are not well characterized. Your observations may be very useful in improving our understand of these objects. As with BM Ori, 2-3 cycles of BVRI per night would be most useful. In order to reach fainter magnitudes, it would be necessary to saturate on BM Ori, or else take multiple exposures and co-add. Observers should use the "126" comparison star as the reference for fainter objects.

3) Observations of targets of interest outside the Trapezium. There are a number of targets in and around Orion but outside the Trapezium region that are of astrophysical interest, and any and all young stellar objects in Orion, Taurus, and Auriga are welcome. For both visual and CCD observers, there are a number of rapid and irregular variables whose light curves are deserving of long-term monitoring and have been a part of the AAVSO program for many decades. These include: T Ori, UX Ori, FU Ori, T Tau, RR Tau, RY Tau, and RW Aur. All of these sources have had excellent visual coverage which should continue for the indefinite future. Calibrated BVRI observations of these targets would also be valuable, and again should concentrate on photometric precision rather than rapid cadence.

For all of these sets of targets, please use your best judgment as to what your optimal exposure times are to obtain the best signal-to-noise without saturating. CCD observers may wish to take advantage of the fact that a number of the sources in a given field are variable; if your data clearly show variability in a suspected variable or previously unknown variable, please submit this information to VSX:http://www.aavso.org/vsx[4]